While no one would ever need an excuse to visit the New York Transit Museum, September 25th is a great day to visit. Firstly, admission will only be 1$ at the Brooklyn location (Grand Central Station has a small exhibition area as well a store, the Downtown Brooklyn location is the main facility including their collection of transit vehicles). Secondly, it is the Bus Fest. Over a dozen of their vintage buses will outside on display.
For more info on Bus Fest: http://www.nytransitmuseum.org/BusFest/
New York Transit Museum: http://www.nytransitmuseum.org